1. Field of the Invention
The present invention provides a system for transferring liquid from one location to another while preventing the siphoning of the liquid through the system opposite the intended direction of flow. More particularly, the present invention provides a system for transferring water from a transfer canal to a spent fuel pool in a nuclear reactor facility, the system preventing the siphoning of water from the spent fuel pool, which may contain radioactive contaminants, back into the transfer canal.
2. Description of the Prior Art
The transfer of liquid between locations that are at different levels or heights creates the potential problem of liquid being siphoned between the two locations. In many applications, siphoning is unacceptable and adequate measures must be taken to prevent its occurrence. This need is particularly important where radioactive materials are involved and the possibility of contamination is present, such as in a nuclear reactor facility where water must be transferred into the spent fuel pool. The spent fuel pool is a large tank with racks to hold spent nuclear reactor material. The pool is filled to a specified level with water. Trace chemical elements present in the water may become radioactive in the presence of the reactor material over time. It is important that the water level in the spent fuel pool be kept within specific limits. Water must be added at times to maintain the proper water level within these limits for cooling and safety reasons. The source for additional water is typically a transfer canal. The water and any dissolved trace elements in the transfer canal to be added are not radioactive. It is desirable for safety and contamination prevention not to have water from the spent fuel pool siphoned back into the transfer canal. Otherwise, there is the potential for radioactive contamination of water in the transfer canal, as well as causing of an undesirable decrease of the water level in the spent fuel pool.
One technique for prevention of siphoning is shown in U.S. Pat. No. 5,046,529 (Corella), which describes a potable water system having a container with an internally disposed standpipe. The standpipe has an anti-siphon port near the top to prevent the backflow of water from within the container out through the inlet flow line. A significant disadvantage of this system is that the water level inside the container may rise to a level above the port in the standpipe, and water in the container could then flow out through the inlet flow line. Clearly, this type of system would be unsatisfactory for use in a nuclear facility, as backflow, in any amount, presents a contamination hazard and is therefore unacceptable.
Another system is shown in U.S. Pat. No. 5,268,942 (Newton), which is directed to a temporary cooling system for use in nuclear power plants. The system includes an anti-siphon mechanism in the form of one or more anti-siphon holes in the primary pump suction line. However, the location of the anti-siphon holes is below the maximum water level, thereby allowing at least some amount of water to back flow through the system.
The use of one-way valves and check valves have also been used in attempted prevention of siphoning. For instance, U.S. Pat. No. 3,951,164 (Crist) describes a relatively complex antisiphon and backflow prevention valve. The valve comprises a check valve and an air valve inside a valve body. The use of a complex valve with a large number of parts increases the cost and reduces the reliability of such a system. In a nuclear facility, reliability is of paramount importance. Many systems in a reactor facility are not used until an emergency condition arises. However, they must be in proper working order, even after sitting dormant for relatively long periods of time.
An air gap anti-siphon system for drainage of waste water from a water treatment system to a drain line is shown in U.S. Pat. No. 5,592,964 (Traylor), with an air gap anti-siphon system capable of blocking a sudden sewage backflow. This is accomplished through the use of a disk and tube apparatus fitted into the system. So far as is known, this sewage treatment system with complex and additional apparatus has not been suitable for use in a radioactive material system where a high degree of reliability is necessary.